Instant communication is rapidly becoming a virtually indispensable part of daily life, particularly in the conduct of business. Communication systems today carry both voice information and data to virtually any place on this planet. Through the international telephone system, a person can contact and carry on a conversation with another person thousands of miles away. Using either the international telephone system or dedicated communication lines, data can be transferred between widely separated computers or other electronic devices.
In many situations, a number of telephone sets or other communication devices are present at a single location. Besides having access to the outside telephone system, these devices should be able to communicate among themselves as an intercom, without needing to resort to the external system. A number of systems have been proposed to provide that dual capability.
The most common systems require a central processor or controller to coordinate the communications among the individual sets. Such central controllers tend to make these systems expensive, and may cause difficulties in adding or deleting individual sets from the system.
Another type of system that may include a central controller, or may be a peer-to-peer system with no central control, allows one set to establish communications with another, then preclude the use of the intercom line by the other units in the system. Priority may be based on which set dials up on the system first, or may be pre-established among the sets. These systems may include complicated control techniques to ensure priority is properly established. Data storage may need to be provided either in the lower-priority communication set or in the processor attached to that communication set to hold data until the intercom line is freed.
To provide simultaneous intercom communication between more than one pair of communication sets, other systems use a large number of conductors to connect the sets. Such systems obviously require extensive wiring at the location in which the system is located.